How can I make a Portserver or Digi One product kill an orphaned socket automatically?

First of all, make sure you are using 3.1.12 or 3.1.13 firmware version. If you get a syntax error when trying the commands below, you most likely need to upgrade firmware (or recheck your syntax). Here is the formula of how this works:
idle time + (probe_cnt * probe_interval) = total timeout value

#> set tcp keepalive_idle=00:00:10 probe_count=5 probe_interval=10 rto_max=10

This will make the unit kill an unresponsive tcp socket connection after about 50 seconds of idle/inactivity/server out to lunch. Another inbound socket connection would then be able to make a socket connection to the port. Note that the default value of the Portserver is 2 hours.

This is a good balance of tolerance vs. annoyance, i.e. you want to set this long enough that a spike in network lag does not kill an active socket connection, but a truly orphaned socket will still be killed promptly.

To set it to 2-3 minutes, just back off the values in set tcp. 5/10 is 50 seconds. 5/30 would be 2.5 minutes.

Here are the various settable options/units:

#> set tcp ?

Sets/displays tcp configurations.

syntax: set tcp [Options...]

Options: realport=(tcpport#)                  rto_max=(number){1-240}
ockets=(number){2000-9000}               keepalive_idle=(hour.minute.second) (0.0.10 - 24.0.0)
robe_count=(number){5-30}                 probe_interval=(number){10-75}